Control apparatus



na-1943 i w, DAWSON 2315,602

CONTROL Al PARATUS Original Filed May 7, 1938 2 Sheets-Sheet 1 if Q. 1. i '59 i W|TNESSES: i I T Jafm M/Dawsan;

ATTORNEY April 6, 1943. J, W, DAWSON 2,315,602

CONTROL APPARATUS Original Filed May 7, 1958 2 Sheets-Sheet 2' 7 -1a'0 9'0 K30 V0 [rage Dz'z/z'de 56127779 I INVENTOR I John Wflawsan.

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WITNESSES:

Patented Apr. 6, 1943 T oF icE coN'raor. APPARATUS John W. Dawson, Auburndale, Mass., assignor to Westinghouse Electric 8; Manufacturing Company, East Pittsburgh,

Pennsylvania,

Pa., a corporation of Original application May 7, 1938, Serial No.

206,640. Divided and this application 1941, Serial No. 402,499

5 Claims.

My invention relates to control apparatus and has particular relation to apparatus for precisely varying the supply of power to a load.

The present application is a division of my application, Serial No. 206,640, filed May 7, 1938,

and assigned to the Westinghous Electric 8: Manufacturing Company. 7

My invention has particular applicability to welding apparatus in which the welding current supplied must be varied over a wide range to accommodate the diiferent properties of the materials to be welded. In resistance welding apparatus constructed and operated in accordance with the teachings of the prior art of which I am aware, current is supplied for welding purposes from an alternating-current source during selected half periods of the source. The time during which welding current is supplied is measured in terms of half-periods of the source; To vary the welding heat, the instant of initiation of the supply of current in each of the half periods of the source is varied. The selection of a number of half-periods for any welding operation shall be designated herein as the timing of the welding operation. The setting of the instants in the half-periods when current flow is initiated shall be designated herein as heat-control.

Timing and heat control in welding involves the use of valves which permit current flow. to the welding load, at most, during a half period of the source. In the apparatus of the prior art, the flow of current through the valves is initiated by impressing initiating impulses on the valves. The welding is timed by supplying initiating impulses during a certain number of selected half-periods; the heat is controlled by setting the instant in each half period at which the corresponding initiating impulse becomes efiective. The phase angle at which the initiating impulses become effective in the half cycles of the source is customarily determined by a phase shift network of the usual type. Such a network comprises a pair of dephasing impedances connected in series across a source and some means for, in effect, deriving the potential existing between any desired point on either of the impedances and an intermediate output tap of the source.

In apparatus constructed in accordance with the teachings of the prior art, a voltage divider is connected in parallel with the whole series im pedance network and one of the output terminals of the phase shift system is the variable tap of the voltage divider. However, I have found that as the variable tap of the voltage divider is moved from point to point, the currentsupplied July 15,

to the loaddoes not vary uniformly with the setting of thetap. As a matter of fact, for considerable portions of the available path of movement of the tap, particularly at the twoends thereof, the change in the current flow produced is inappreciable for different settings of the tap.

A relatively small portion of the voltage divider,

therefore, actually serves a useful purpose.

It is accordingly,an object of my invention to provide a phase shiftnetwork wherein it shall I be possible to select any desired portion of'a half cycle for the range of control.

Another object of my invention is to provide a system incorporating a voltage divider for controlling the current flow from a source of peri odic pulsations through a load by controlling the points of initiation of current flow during each of the pulsations, wherein the magnitude of the current shall be a substantially uniformly varying function of the distance of the putput oi the variable tap of the voltage divider from its ends.

More generally stated, it is an object of my invention to provide a contrivance for controlling the initiation of current flow from a source of periodic pulsations to a load at diiferent points in the pulsations, incorporating an impedance for attaining the desired control, wherein over the whole range of the impedance, the current supplied to the load shall be a substantially linear function of the setting of the impedance.

7 According to my invention, I connect the voltage divider whereby the current fiow through the load is to be varied between connecting points of the phase shift impedance elements that are intermediate the ends thereof. The connecting points are so selected that the current flow through the load will vary as a substantially linear function of the setting of the voltage divider over the whole'range of the voltage divider. The intermediate connecting point of one of the clephasing impedances to which the voltage divider is connected is selected to correspond to a value of load current of such small magnitude that it produces no appreciable eifect on the load apparatus. The intermediate connecting point of the other dephasing impedance is such that with the voltage divider set at this point the current ilow isinitiated at instants in the pulsations I of the source which correspond to substantially the maximum current which may flow through the load, taking into consideration its power factor. Since welding loads have power factors with a number of intermediate connecting points, each of which corresponds to a diiferent power factor.

The novel features that I consider characterunderstood from the following description of a specific embodiment, when read in connection with the accompanying drawings, in which:

Figure 1 is a diagrammatic view showing a preferred embodiment of my invention;

Fig. 2 is a graph showing the relationship between the settings of the voltage divider and the load current in the prior art apparatus;

Fig. 3 is a graph showing the relationship between the load current and the settings of the voltage divider in apparatus constructed according to my invention; and

Fig. 4 is a graph showing the relationship between the power factor and the settings of one of the dephasing impedances.

The apparatus shown in Figure 1 comprises a welding transformer 5, from the secondary 1 of which current is supplied to weld a material 9 through a pair of suitable electrodes II. The primary i3 of the welding transformer is supplied from a suitable source 15 through a pair of discharge paths l1 and 19 connected in antiparallel. Each of the paths comprises an anode 2|, a mercury-pool cathode 23, and an ignition electrode 25 of boron-carbide or a similar material which dips into the mercury. Current is supplied to the welding transformer through the discharge paths i1 and I9, each path carrying a current pulse during a half period.

The flow of current through the discharge paths is initiated at predetermined points in the half periods of the source by impressing impulses on the ignition electrode 25 of each path in its turn. When once initiated during any half period, the current continues to flow until a short time after the half period, the length of which is determined by the power factor of the load. The number of half periods during which current flow takes place is selected by the operation of a magnetic impulsing device described in detail in my Patent No. 2,081,987, for Electric control systems, issued June 1, 1937, and assigned to the Westinghouse Electric 8: Manufacturing Com pany.

Briefly, the selection takes place by supplying the ignition impulses for the discharge paths" and 19 through timing electric discharge devices 21 and 29. Each timing device has an anode 3!, a cathode 33, a control electrode 35. and a gaseous medium. The timing devices 21 and 29 are rendered conductive during the selected half periods by impulses impressed between their respective control electrodes 35 and cathodes 33 from a magnetic impulsing device 31. The latter comprises a permanent magnet core 39 of rectangular form having an air gap 4| over which a disc 43 is rotated in synchronism with the source 15. In the periphery of the disc, pins 45 are inserted so that they pass through the air gap 4| during the selected half periods and induce potential impulses in coils 41 and 49 wound on the core. The coils 41 and 49 are connected in the control circuits 5! and 53. respectively, of the timing devices 21 and 2.9 in the usual well known manner.

A second pair of electric discharge devices 55 and 81, which I shall herein designate as heat control devices is provided to set the points in the half periods at which the main discharge paths are rendered conductive. Each of the heat control devices comprises an anode 89, a cathode 8!, a control electrode 83 and a gaseous medium. A heat control device and a timing device are connected in series with an ignition electrode of each of the main discharge paths. For the path I1 this circuit extends from the lower supply conductor 65, through a conductor 61, a current limiting resistor 69, the anode 59 and the cathode 5| of the left-hand heat control device 51, a conductor 11, a conductor 13, the anode 3| and the cathode 33 of the left-hand timing device 21, a conductor 15. the ignition electrode 25 of the path 11, the cathode 23, a conductor 11 and the primary i 3 of the upper supply conductor 19.

The heat control devices 51 and 59 are controlled from a phase shift network 8| through control transformers 83 and 85, respectively. The network comprises a parallel-connected resistor assembly 81 connected in series with a reactor 88 across the secondary 9| of an auxiliary transformer 93. In lieu of the resistors 81 and the inductive reactor 89 actually used, dephasing impedances of other types may be utilized. Thus for example, the reactor may be replaced by a capacitor.

The resistor assembly 91 is provided with an intermediate connecting point 95 and the reactor is provided with a plurality of such intermediate points 91. A voltage divider 99 is connected between the intermediate connecting point 99 of the resistors 81 and one of the points 91 of the reactor 89. The potential output between the variable tap I01 of the voltage divider 99 and an intermediate tap I03 of the secondary 9i of the auxiliary transformer 93 is supplied to the primaries I95 of the control transformers 83 and 85. The variable tap IN is connected to the common junction point of one of the terminals of each of the primaries I05 and the intermediate tap N13 is connected to a point on a balancing resistor I91 that is connected between the other terminals of the primaries.

The settings of the variable tap Ifll of the voltage divider 99 correspond to different phases of the potential impressed on the secondaries "8 of the control transformers 83 and 85. Over the whole voltage divider the phase of the potential impressed varies from an angle corresponding to the intermediate connecting point 95 of the resistors 81 to an angle corresponding to the selected intermediate connecting point 91 of the reactor 89. Th secondaries I09 of the transformers 83 and are connected between the control electrodes 59 and the cathodes ii of the heat control devices 51 and 59, respectively, and the potential of these secondaries is, therefore, impressed in the corresponding control circuits I H and H3.

The potentials thus impressed in the control circuits of the heat control devices 51 and 99 from the phase shift network have the eflect of rendering the heat control devices conductive at points in the half cycles corresponding to the settings of the voltage divider 99. The pins 49 moving through the air gap in the core 39 impress potentials to render the timing devices 21 and 29 conductive during the selected half periods. The timing devices 21 and 29, however, are rendered conductive at points in the half periods that are earlier than the earliest points at which the heat control devices 51 and 59 are the half periods,

. aaracoa rendered conductive. Accordingly, resistors Ill and III are connected to shunt the heat control devices 51 and 59, respectively, thus affording paths for the current from the timing devices to flow when they are conductive, while the heat control devices are still non-conductive. The resistors H and ill are, of course, of such magnitude that the main paths i1 and is are not rendered conductive by the current which flows through the resistors and the ignition electrodes When th heat control devices 51 and 59 are rendered conductive at the selected instants in substantial current flows through the associated ignition electrodes 25 and the corresponding main discharge paths i1 and ii, respectively, are rendered conductive. Welding current is thus conducted for a number of half periods predetermined by the arrangement of the pins 45 in disc 43 and during portions of the half periods predetermined by the setting of the voltage divider 89. By varying the setting of the variable tap IOI of the voltage divider 99,

setting of the variable tap iiii over the whole range of the voltage divider 99. It is to be noted, however, that while linearity is, in general, the

condition desired, there are cases in which the welding current may be other than a linear function of the setting of the tap "II. My invention includes such cases within its scope when the selection of the connecting points 95 and 91 is such that over the whole range of the voltage divider 99 there is a substantial increase in current for each successive operation.

In selecting the intermediate connecting points 95 and 91, th properties of the apparatus must be taken into consideration. The interme-, diate connecting point .95 of the resistors I1 is selected so that if the variable tap NH of the voltag divider 99 coincides electrically with it, the current transmitted through the load 9 will be too small to produce any appreciable welding effect. The intermediate connecting points 91 of the reactor is are selected to correspond to the maximum possible current flow for the particular load that is being supplied. The maximum current is that which flows when the discharge paths i1 and is are rendered conductive at angles in the half cycles, which correspond to the power factor angle of the load. The intermediate connecting points 91 of the reactor, therefore, correspond tothe different power factors which different loads would have.

The advantageous aspectsof the invention are illustrated in Figs. 2 and 3. In Fig. 2 the percent of maximum current is plotted as a function of the setting of the voltage divider for the prior art apparatus. It will be noted that the useful range of the voltage divider, constituting the straight line portion N9 of the curveili which extends approximately from the setting 26 to the setting 46 constitutes a relatively small portion of the whole voltage divider. For a given length of voltage divider, therefore, a considerable portion is not used for any purpose and goes to waste. Fig. 3 is a corresponding plot for a system in accordance with my invention. The

different curves I23, I25 and I21 correspond to different power factors as indicated. For purposes of comparison, a straight line I29 passing through points in the neighborhood of those corsubstantially linear function of the setting. It

will be noted that in an arrangement corresponding to Fig. 3, substantially the whole range of the voltage divider is used.

g In the operation of my invention the power I factor of the load 9 may be determined by any test well known in the art, as for example, by using a power factor meter. The left-hand end of the voltage divider 99 is then connected to a point 91 of the reactor 89 which corresponds to the power factor in question. The tap required may be derived from a curve i3i such as is shown in Fig. 4. in which the percent of the length of the reactor 89 is plotted as a function of the power factor.

With the voltage divider 99 connected as described above, its variable tap illl may be set at a point along it corresponding to the desired current flow with considerable accuracy, since the whole range of the divider is available for the setting.

The voltage divider 99 is customarily provided with a scale 200 preferably having uniformly spaced indications 202. By reading thescale the operator can at once note what percent of the maximum current will flow through the material for the corresponding setting of the voltage divider. In apparatus constructed according to the teachings of the prior art, the indications of the scale may beset to yield this information with any accuracy at all for a load of only one selected power factor. For different power factors than the one selected to correspond to the scale there is a material difference between the percent of maximum current to which the readings of the scale should correspond and those to which they actually do correspond. By provlding the different connecting points 91 on the reactor 89 to correspond to different power factors, I eliminate this difference. With the voltage divider 99 connected to the point 91 that corresponds to the power factor of the load actually in use the scale divisions indicate accurately the percent of the maximum current which is flowing for the load.

Although I have shown and described certain specific embodiments of my invention, I am fully aware that many modifications thereof are possible. My invention, therefore, is not to be restricted except insofar as is necessitated by the I prior art and by the spirit of the appended claims. a

I claim as my invention:

1. A phase shift network comprising a source of electric power having a plurality of taps, a

pair of dephasing impedances connected in series I I r oi electric power having a plurality oi taps, a pair of dephasing impedances connected in series between a pair or the taps or said source. each oi said impedances having an intermediate connecting point, a voltage divider having an adjustable tap connected between said points, and

means for deriving a potential between the adjustable tap of said divider and a tap of said source other than the pair to which said impedances are connected.

3. A phase shift network comprising a source of alternating current having a, plurality of taps, a pair of dephasing impedances connected in series between a pair of the taps of said source, each of said impedances havilng an intermediate connecting point, a voltage divider having an adjustable tap connected between said points, and means for deriving a potential between the adjustable tap of said divider and one of the taps or said source.

4. A phase shift network comprising a source of electric power having a plurality 0! end taps and an intermediate tap, a pair or dephasing impedances connected in series between said and taps, each 01' said impedances having an intermediate connecting point, a voltage divider having an adjustable tap connected between said points, and means ior deriving a potential between the adjustable tap of said divider and said intermediate tap of said source.

5. A phase shift network comprising a source of electric power having a plurality of taps, ohmic resistance means and reactance means connected in series between a pair of the taps of said source, said resistance means and said reactance means each having an intermediate connecting point, a voltage divider having an adiustaable tap connected between said points, and'means for deriving a potential between the adjustable tap of said divider and one of the taps of said source.

JOHN W. DAWSON. 

